-----Original Message-----
From: jeff@inf.ed.ac.uk
To: David Martin
Cc: Amit Sheth @ LSDIS; public-sws-ig@w3.org
Sent: 11/19/05 4:30 PM
Subject: Re: Options we have with respect to the draft charters (i.e., RE:
[fwd] Draft charters for work on Semantics for WS)
BTW, why is it said that "the current WSDL standard operates at the
syntactic level"? What is any more semantic about the things that
are labelled "semantic"?
WSDL operates at the syntactic level because it only contains the names of
the object data types and functions, etc. that are used developing the
service, as well as the object hierarchy, relations, etc. which are ALL of
the outcomes generated in Object Oriented Programming (OOP) approach. This
means, WSDL contains the details of coding process generated by OOP,
however, the meaning (semantics) of the service is not described and defined
within WSDL.
Given in the typical and classic example (as I mentioned many many times in
this group) of ESRI's Address Finder Web Service,
http://arcweb.esri.com/services/v2/AddressFinder.wsdl
the meaning (semantics) of this Web service is:
if the requester can invoke ESRI's authentication Web service to obtain a
validated token string, then requester can use this token string with the
input "address" object data type as well as the specified data source to
invoke Address Finder Web Service, which will then return the location(s)
(longitude and latitude) that can match the input address or will then
return an error message to the requester. Details in
http://www-128.ibm.com/developerworks/webservices/library/ws-semantic/
Unfortunately, nobody can find the service semantics within this WSDL file.
Then what and how can WSDL-S deal with describing the semantics of such
existing Web services?
First, let's see the definition offered by WSDL-S at
http://www.w3.org/Submission/WSDL-S/:
"Semantics in this context refers to the meaning of objects or information."
Semantic annotations in WSDL-S "define the meaning of elements in WSDL
document by referring to a part of a semantic model".
This means "Semantics" in WSDL-S is the meaning of objects used in WSDL
elements (generated by OOP) rather than the meaning of service (may have
nothing with OOP or WSDL). Thus WSDL-S handles the content within WSDL, but
unfortunately, the meaning of service is beyond the WSDL document itself, as
demonstrated by the Address Finder Web Service. In this case, we have to add
semantic annotation onto "token" elements to tell requesters that they have
to invoke another Web service before they use this one.
More specifically, given the example in Address Finder Web Service, what
requesters want to know should be the location(s) (x,y cordinate values)
that may match the input address. However, before they can retrieve the x,y
coordinate values, they have to generate the following objects (as described
in WSDL) first:
1. LocationInfo object, which contains another 4 data types/elements in
which
2. ArrayOfLocation object contains (as well as some other elements)
3. an array of Location[] objects, which have (as well as some other
elements)
4. a Point property that contains
5. the x, y values (and the coordinateSystem object).
Except the x, y values and coordinate system information, all other objects
and information in WSDL may be meaningless and useless to the requesters. I
wish WSDL-S people were able to explain whether WSDL-S would like to add
semantic annotation onto ALL WSDL elements (in this case, we may waste time
to define something that is useless and meaningless to the requesters), or
just onto a few meaningful elements (in this case, the WSDL file may be a
mess since most parts are not defined while only a few elements have
semantic annotations).
Considering W3C defines Web service as that "A Web service is a software
system designed to support interoperable machine-to-machine interaction over
a network", since interoperable machine-to-machine interaction (Web
services) can be implemented over a network by different approaches, WSDL-S
just handles one case in such broad domain applications then, this WG has to
handle such challenges beyond WSDL Web services if people in this WG
acknowledge such a fact.
As for David Martin's suggestinos to "bridge between the Web service and
Semantic Web efforts at W3C", I think they can be connected and unioned via
HTTP without adding extra mechanisams on top of HTTP as demonstrated in
those cases I discussed in
http://lists.w3.org/Archives/Public/public-sws-ig/2005Nov/0040.html